Question 1

Which of the following best describes chemical equilibrium in a closed system?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

For the reaction $$\ce{N2(g) + 3H2(g)  2NH3(g)}$$, the equilibrium constant expression $$K_c is$$:

Accepted Answer

$$K_c = \frac{[\ce{NH3}]^2}{[\ce{N2}][\ce{H2}]^3}$$

Question 3

If the equilibrium constant $$K$$ for a reaction is much greater than 1, what does this indicate about the reaction at equilibrium?

Accepted Answer

Products predominate.

Question 4

For the reaction $$\ce{2SO2(g) + O2(g)  2SO3(g)}$$, if the equation is reversed, what happens to the equilibrium constant?

Accepted Answer

It becomes the reciprocal.

Question 5

A reaction has $$K_c = 4.0 at a $$certain temperature. If the equation is multiplied by 2, what is the new equilibrium constant?

Accepted Answer

$$K_c = 16.0$$

Question 6

Which of the following is NOT included in the equilibrium constant expression for the reaction $$\ce{CaCO3(s)  CaO(s) + CO2(g)}$$?

Accepted Answer

$$[\ce{CaCO3}]$$

Question 7

Given the reaction $$\ce{H2(g) + I2(g)  2HI(g)}$$ with $$K_c = 50.5 at 448$^\circC$$, if $$[\ce{H2}] = 0.065 M$$, $$[\ce{I2}] = 0.065 M$$, and $$[\ce{HI}] = 0.870 M$$, is the system at equilibrium?

Accepted Answer

Yes, because $$Q = K.$$

Question 8

If the reaction quotient $$Q is $$less than the equilibrium constant $$K$$, what will happen?

Accepted Answer

The reaction will shift toward products.

Question 9

Which change will NOT affect the value of the equilibrium constant $$K$$ for a given reaction?

Accepted Answer

Addition of a catalyst.

Question 10

For the reaction $$\ce{N2(g) + 3H2(g)  2NH3(g)}$$, which of the following will shift the equilibrium toward the formation of ammonia ($$\ce{NH3}$$)?

Accepted Answer

Increasing the pressure.

Question 11

A catalyst is added to a reaction mixture at equilibrium. What is the effect on the equilibrium position and the equilibrium constant?

Accepted Answer

The equilibrium is reached faster; $$K$$ remains unchanged.

Question 12

In a closed container, the reaction $$\ce{2NO2(g)  N2O4(g)} is at $$equilibrium. If more $$\ce{NO2} is $$added, what will happen according to Le Châtelier’s Principle?

Accepted Answer

The equilibrium will shift to produce more $$\ce{N2O4}.$$

Question 13

For the reaction $$\ce{A(g)  2B(g)}$$, if the volume of the container is doubled, what will happen to the equilibrium position?

Accepted Answer

It will shift toward the side with more moles of gas.

Question 14

Which of the following statements about heterogeneous equilibria is correct?

Accepted Answer

The concentrations of pure solids and liquids are omitted from the equilibrium constant expression.

Question 15

A 1.00 L flask contains 1.00 mol of $$\ce{H2}$$ and 2.00 mol of $$\ce{I2}. At $$equilibrium, $$x$$ mol of $$\ce{H2}$$ has reacted. Write the equilibrium concentration of $$\ce{HI} in $$terms of $$x.$$

Accepted Answer

$$[\ce{HI}] = 2x$$

Question 16

For the reaction $$\ce{2SO2(g) + O2(g)  2SO3(g)}$$, how does increasing the temperature affect the equilibrium if the reaction is exothermic?

Accepted Answer

The equilibrium shifts toward reactants; $$K$$ decreases.

Question 17

Which of the following is a correct statement about the reaction quotient $$Q$$?

Accepted Answer

$$Q is $$calculated using current concentrations, not necessarily at equilibrium.

Question 18

If the equilibrium constant for a reaction is $$K_c = 1.0 	imes 10$$^{-5}$$, which of the following best describes the mixture at equilibrium?

Accepted Answer

Mostly reactants are present.

Question 19

Which of the following best explains why equilibrium constants are unitless?

Accepted Answer

Because the units cancel out due to the way the equilibrium expression is written.

Chemical Equilibrium: Principles, Calculations, and Applications

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